U.S. patent application number 11/456104 was filed with the patent office on 2007-02-01 for light source apparatus, exposure apparatus and device fabrication method.
Invention is credited to Kazuki FUJIMOTO, Jun ITO, Hajime KANAZAWA, Yutaka WATANABE.
Application Number | 20070023709 11/456104 |
Document ID | / |
Family ID | 37693318 |
Filed Date | 2007-02-01 |
United States Patent
Application |
20070023709 |
Kind Code |
A1 |
KANAZAWA; Hajime ; et
al. |
February 1, 2007 |
LIGHT SOURCE APPARATUS, EXPOSURE APPARATUS AND DEVICE FABRICATION
METHOD
Abstract
A light source apparatus for generating a plasma and supplying a
light irradiated from the plasma to an optical system, said light
source apparatus includes a chamber for accommodating a region that
generates the plasma, wherein a density of a hydrocarbon compound
included in a gas in the chamber is 300 ppb or less.
Inventors: |
KANAZAWA; Hajime;
(Utsunomiya-shi, JP) ; WATANABE; Yutaka;
(Shioya-gun, JP) ; ITO; Jun; (Utsunomiya-shi,
JP) ; FUJIMOTO; Kazuki; (Utsunomiya-shi, JP) |
Correspondence
Address: |
MORGAN & FINNEGAN, L.L.P.
3 WORLD FINANCIAL CENTER
NEW YORK
NY
10281-2101
US
|
Family ID: |
37693318 |
Appl. No.: |
11/456104 |
Filed: |
July 7, 2006 |
Current U.S.
Class: |
250/504R |
Current CPC
Class: |
G03F 7/70033 20130101;
H05G 2/005 20130101; G03F 7/70983 20130101; G03F 7/70916 20130101;
H05G 2/003 20130101; H05G 2/006 20130101; B82Y 10/00 20130101 |
Class at
Publication: |
250/504.00R |
International
Class: |
G01J 3/10 20060101
G01J003/10 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 8, 2005 |
JP |
2005-200764(PAT.) |
Claims
1. A light source apparatus for generating a plasma and supplying a
light irradiated from the plasma to an optical system, said light
source apparatus comprising a chamber for accommodating a region
that generates the plasma, wherein a density of a hydrocarbon
compound included in a gas in the chamber is 300 ppb or less.
2. A light source apparatus for generating a plasma and supplying a
light irradiated from the plasma to an optical system, said light
source apparatus comprising a supplier for supplying a material to
generate the plasma, wherein a density of a hydrocarbon compound
included in a material supplied to generate the plasma is 300 ppb
or less.
3. A light source apparatus according to claim 2, wherein a density
of a hydrocarbon compound included in a fluid material supplied to
prevent a reach of debris generated from the plasma to the optical
system is 300 ppb or less.
4. A light source apparatus for generating a plasma and supplying a
light irradiated from the plasma to an optical system, said light
source apparatus comprising: a first supply pipe for supplying a
material to generate the plasma; and a first filter, provided to
the first supply pipe, for improving a purity of the material.
5. A light source apparatus according to claim 4, further
comprising: a second supply pipe for supplying a buffer gas that
prevents a reach of debris generated from the plasma to the optical
system; and a second filter, provided to the second supply pipe,
for improving a purity of the buffer gas.
6. A light source apparatus according to claim 4, wherein said
first filter improves a density of a hydrocarbon compound included
in the material to 300 ppb or less.
7. A light source apparatus according to claim 5, wherein said
second filter improves a density of a hydrocarbon compound included
in the buffer gas to 300 ppb or less.
8. A light source apparatus according to claim 4, wherein said
first supply pipe consists of metal at least between the first
filter and a supply port that supplies the material.
9. A light source apparatus according to claim 5, wherein said
second supply pipe consists of material at least between the second
filter and a supply port that supplies the buffer gas.
10. A light source apparatus according to claim 4, wherein said
first filter is provided at a side of a supply port that supplies
the material rather than a side of a supply source of the
material.
11. A light source apparatus according to claim 5, wherein said
second filter is provided at a side of a supply port that supplies
the buffer gas rather than a side of a supply source of the buffer
gas.
12. An exposure apparatus comprising: a light source apparatus
according to claim 1; an illumination system for illuminating a
pattern of a mask using a light from the light source; and a
projection system for projecting the pattern onto a plate.
13. An exposure apparatus comprising: a light source apparatus
according to claim 2; an illumination system for illuminating a
pattern of a mask using a light from the light source; and a
projection system for projecting the pattern onto a plate.
14. An exposure apparatus comprising: a light source apparatus
according to claim 4; an illumination system for illuminating a
pattern of a mask using a light from the light source; and a
projection system for projecting the pattern onto a plate.
15. A device fabrication method comprising the steps of: exposing a
plate using an exposure apparatus according to claim 12; and
performing a development process for the plate exposed.
16. A device fabrication method comprising the steps of: exposing a
plate using an exposure apparatus according to claim 13; and
performing a development process for the plate exposed.
17. A device fabrication method comprising the steps of: exposing a
plate using an exposure apparatus according to claim 14; and
performing a development process for the plate exposed.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates generally to an exposure
apparatus, and more particularly to a light source apparatus used
in an exposure apparatus for exposing an plate, such as a single
crystal substrate of a semiconductor wafer etc. and a glass plate
for a liquid crystal display ("LCD"). The present invention is
suitable, for example, for an exposure apparatus that uses an
extreme ultraviolet ("EUV") light as a light source for
exposure.
[0002] A reduction projection optical system using an EUV light as
an exposure light (referred to as an "EUV exposure apparatus"
hereinafter) has been developed to manufacture a fine semiconductor
device that has very fine circuit pattern of 0.1 .mu.m or less. The
EUV light is a light with a wavelength of 10 nm to 15 nm shorter
than that of an ultraviolet light.
[0003] The EUV exposure apparatus typically uses a laser plasma
light source and a discharge plasma light source as the light
source. See, for example, Japanese Patent Applications, Publication
Nos. 2002-174700 and 2003-077698. The laser plasma light source
irradiates a laser beam to a target material to generate a plasma
and generates the EUV light. The discharge plasma light source
generates a plasma by introducing gas to an electrode for
discharging and generates the EUV light. The EUV light from the
plasma is condensed at a condensing point, diverges from the
condensing point, and enters a subsequent illumination optical
system via an opening formed between the light source and the
illumination optical system.
[0004] However, a material necessary for an emission, i.e., the
target material or discharge gas, is supplied to a light source
chamber that accommodates the plasma (an emission part). Therefore,
an impurity included in those materials flows into the light source
chamber. A hydrocarbon included in the impurity adheres a carbon as
a contaminant to a part irradiated by the EUV light, and reduces a
reflectance of an optical element, such as a condensing mirror.
[0005] Moreover, it is preferably to provide a window material that
functions as a vacuum partition at the opening (connecting part)
between the light source and the illumination optical system.
However, a material that penetrates the EUV light or a material
that can fully resist a heat load by the EUV light of power
necessary for exposure does not exist. Therefore, the hydrocarbon
included in the material necessary for the emission flows into a
chamber that accommodates the illumination optical system and a
projection optical system via the opening, adheres the carbon to an
optical element in the illumination optical system and the
projection optical system, and reduces the reflectance. Moreover, a
light intensity on a target surface to be illuminated becomes
non-uniformly according to an adhesion state of the carbon to the
optical element. As a result, a decrease of throughput and
resolution is caused.
BRIEF SUMMARY OF THE INVENTION
[0006] Accordingly, the present invention is directed to a light
source apparatus that can reduce a contamination of an optical
element in a subsequent optical system.
[0007] A light source apparatus of one aspect of the present
invention for generating a plasma and supplying a light irradiated
from the plasma to an optical system, said light source apparatus
includes a chamber for accommodating a region that generates the
plasma, wherein a density of a hydrocarbon compound included in a
gas in the chamber is 300 ppb or less.
[0008] A light source apparatus according to another aspect of the
present invention for generating a plasma and supplying a light
irradiated from the plasma to an optical system, said light source
apparatus includes a supplier for supplying a material to generate
the plasma, wherein a density of a hydrocarbon compound included in
a material supplied to generate the plasma is 300 ppb or less.
[0009] A light source apparatus according to still another aspect
of the present invention for generating a plasma and supplying a
light irradiated from the plasma to an optical system, said light
source apparatus includes a first supply pipe for supplying a
material to generate the plasma, and a first filter, provided to
the first supply pipe, for improving a purity of the material.
[0010] An exposure apparatus according to still another aspect of
the present invention includes the above light source apparatus, an
illumination system for illuminating a pattern of a mask using a
light from the light source, and a projection system for projecting
the pattern onto a plate.
[0011] A device fabricating method according to still another
aspect of the present invention includes the steps of exposing a
plate using the above exposure apparatus, and performing a
development process for the plate exposed.
[0012] Other objects and further features of the present invention
will become readily apparent from the following description of the
preferred embodiments with reference to the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a schematic sectional view of a light source
apparatus of one aspect according to the present invention.
[0014] FIG. 2 is a schematic sectional view of a light source
apparatus that is variation of the light source apparatus shown in
FIG. 1.
[0015] FIG. 3 is a schematic sectional view of an exposure
apparatus of one aspect according to the present invention.
[0016] FIG. 4 is a flowchart for explaining a method for
fabricating devices (semiconductor chips such as ICs, LSIs, and the
like, LCDs, CCDs, etc.).
[0017] FIG. 5 is a detail flowchart of a wafer process in Step 4 of
FIG. 4.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] With reference to the accompanying drawings, a description
will be given of a light source apparatus of one aspect according
to the present invention. In each figure, the same reference
numeral denotes the same element. Therefore, duplicate descriptions
will be omitted. Here, FIG. 1 is a schematic sectional view of a
light source apparatus 1 of the present invention.
[0019] The light source apparatus 1 is a light source apparatus
that generates a plasma PL and supplies an EUV light EL irradiated
from the plasma PL (a light with a wavelength of 20 nm or less,
preferably, a light with a wavelength of 13 nm or more and 15 nm or
less) to a subsequent optical system 50. The light source apparatus
1 is, in the instant embodiment, a discharge plasma light source.
However, the light source apparatus 1 is not limited to the
discharge plasma light source and may be a laser plasma light
source or a light source of other method.
[0020] The light source apparatus 1 includes an electrode 12, a
first purity improving part 14, a plasma generating part 10 that
has a first supply pipe 16, a condensing mirror 22, a second purity
improving part 24, and a condensing part 20 that has a second
supply pipe 26. The EUV light has a property that is absorbed by
gas. Therefore, the prasma generating part 10 is provided in a
generating chamber GC and the condensing part 20 is provided in a
condensing chamber CC to prevent the absorption. The generating
chamber GC and the condensing chamber CC are exhausted by vacuum
pumping system (not shown) and maintain a predetermined degree of
vacuum. The generating chamber GC and the condensing chamber CC
constitute a light source chamber LC in the instant embodiment.
[0021] The plasma generating part 10 discharges a plasma generating
gas (in the instant embodiment, Xenon (Xe) gas) supplied from the
first supply pipe 16 described later to generate the plasma PL by
high voltage impressed to the electrode 12. The plasma PL with high
density is generated by a pinch action based on a self-magnetic
field of a charged particle flow, and the EUV light EL is
irradiated from the plasma PL.
[0022] The Xe gas as the plasma generating gas is supplied to the
generating chamber GC via the first purity improving part 14 and
the first supply pipe 15 from a Xe tank (not shown) as a supply
source.
[0023] A density of a hydrocarbon compound in the light source
chamber LC (the generating chamber GC and condensing chamber CC
etc.) is 300 ppb or less and preferably 30 ppb or less.
Particularly, a density of a hydrocarbon compound in the condensing
chamber CC is 300 ppb or less and preferably 30 ppb or less.
Therefore, the first purity improving part 14 improves a purity of
the Xe gas, removes the hydrocarbon compound included in the Xe gas
and reduce the density of the hydrocarbon compound in the Xe gas to
300 ppb or less, preferably 30 ppb or less.
[0024] Although the supply pipe (supply system) of the Xe gas is
considered as the main supply source of the hydrocarbon compound in
the instant embodiment, it is considered that the material
basically included in the light source chamber becomes the supply
source of the hydrocarbon compound. In this case, a density of the
hydrocarbon in the gas supplied from the supply pipe of the Xe gas
preferably becomes a density lower than 300 ppb, for example, 200
ppb or less, further preferably, 20 ppb or less.
[0025] The first purity improving part 14 uses, in the present
embodiment, a gas filter that is constituted of an activated carbon
that absorbs the few hydrocarbon compound included in the plasma
generating gas as the impurity. Thereby, the density of the
hydrocarbon compound included in the plasma generating gas that
passes through the activated carbon becomes about 1/100 to 1/1000
of the density of the hydrocarbon compound in the Xe tank as the
supply source. However, the first purity improving part 14 is not
limited to the gas filter that is constituted of the activated
carbon and may be filters, such as a porous metal and a cold trap
that have an absorption function to the hydrocarbon compound.
[0026] In the instant embodiment (in other embodiments), a means to
reduce an amount of the hydrocarbon compound that reaches the
mirror in the subsequent optical system among the hydrocarbon
compound in the light source chamber may be installed. The means
is, for example, a member that absorbs the hydrocarbon compound
(the above cold trap) in the light source chamber or a member that
improves a purity of the Xe gas in the light source chamber
(combination of a gas circulating system and a filter that absorbs
the hydrocarbon compound etc.) etc.
[0027] When the first supply pipe 16 is long, the density of the
hydrocarbon compound of the plasma generating gas easily increases
by a desorption of the impurity from an inner wall of the pipe etc.
Therefore, the first purity improving part 14 is provided near the
generating chamber GC (in other words, near a supply port 16c of
the first supply pipe 16) that is supplied the plasma generating
gas and the influence is preferably reduced as much as
possible.
[0028] The first supply pipe 16 supplies the Xe gas (plasma
generating gas) from the Xe tank (not shown) to the generating
chamber GC via the supply port 16c. The first supply pipe 16
consists of a metal (in the instant embodiment, a stainless steel)
to prevent the desorption of the impurity from the inner wall. The
first supply pipe 16 is preferably given a baking and
vacuum-exhausted a predetermined time to remove a residual gas.
[0029] The first supply pipe 16 consists of the metal such as the
stainless steel irrespective of an inside and outside of the
generating chamber GC because when a resin such as a Teflon tube
that has free form is used as a pipe material, the desorption of
the hydrocarbon compound from the inner wall remarkably increases.
Particularly, the first supply pipe 16 between the first purity
improving part 14 and the supply port 16c needs to consist of the
metal because the first purity improving part 14 cannot remove the
desorption hydrocarbon from the inner wall.
[0030] Moreover, an impurity removal effect of the first purity
improving part 14 has a life and the life becomes short if a gas
with bad purity is used. Therefore, the first supply pipe 16a
between the Xe tank as the supply source and the first purity
improving part 14 preferably consists of the metal.
[0031] In the condensing part 20, the EUV light EL from the plasma
PL pass through a debris filter 30 that removes a debris particle,
is reflected by the condensing mirror 22 that constitutes two
couples of mirrors with a spheroid as a reflective surface, and
condenses at a condensing point CP. The condensing mirror 22 uses a
grazing incidence type mirror in the instant embodiment, but is not
limited to this. For example, the condensing mirror 22 may uses a
normal incidence type mirror that has a multilayer film.
[0032] The debris filter 30 is provided between the generating
chamber GC described later and the condensing chamber CC in the
instant embodiment. The debris filter 30 catches the debris that
generates from the plasma PL or members near the plasma PL and is
intercepted rectilinear propagation by a buffer gas (in the instant
embodiment, an argon (Ar) gas) supplied from the second supply pipe
26 described later. In other words, the debris filter 30 reduces an
amount of the debris and prevents an adhesion of the debris to the
condensing mirror 22 or the optical system 50.
[0033] The Ar gas as the buffer gas is supplied to the condensing
chamber CC from an Ar tank as a supply source (not shown), via the
second purity improving part 24 and the second supply pipe 26. The
buffer gas may be supplied only when the debris particle disperses
by the irradiation of the plasma PL.
[0034] The second purity improving part 24 improves the purity of
the Ar gas, particularly removes the hydrocarbon compound included
in the Ar gas, and becomes the density of the hydrocarbon compound
included in the Ar gas (included in the Ar gas supplied from the
second supply pipe) to 300 ppb or less, preferably 30 ppb or
less.
[0035] The second purity improving part 24 uses, in the present
invention, a gas filter that is constituted of an activated carbon
that absorbs the few hydrocarbon compound included in the buffer
gas as the impurity. Thereby, the density of the hydrocarbon
compound included in the buffer gas that passes through the
activated carbon becomes about 1/100 to 1/1000 of the density of
the hydrocarbon compound in the Ar tank as the supply source.
However, the second purity improving part 24 is not limited to the
gas filter that is constituted of the activated carbon and may be
filters, such as a porous metal and a cold trap that have an
absorption function to the hydrocarbon compound.
[0036] When the second supply pipe 26 is long, the density of the
hydrocarbon compound of the buffer gas easily increases by a
desorption of the impurity from an inner wall of the pipe etc.
Therefore, the second purity improving part 24 is provided near the
condensing chamber CC (in other words, near a supply port 26c of
the second supply pipe 26) that is supplied the buffer gas and the
influence is preferably reduced as much as possible.
[0037] The second supply pipe 26 supplies the Ar gas (buffer gas)
from the Ar tank (not shown) to the condensing chamber CC via the
supply port 26c. The second supply pipe 26 consists of a metal (in
the instant embodiment, a stainless steel) to prevent the
desorption of the impurity from the inner wall.
[0038] Particularly, the second supply pipe 26b between the second
purity improving part 24 and the supply port 26c needs to consist
of the metal because the second purity improving part 24 cannot
remove the desorption hydrocarbon from the inner wall.
[0039] Moreover, an impurity removal effect of the second purity
improving part 24 has a life and the life becomes short if a gas
with bad purity is used. Therefore, the second supply pipe 26a
between the Ar tank as the supply source and the second purity
improving part 24 preferably consists of the metal.
[0040] The EUV light EL reached at the condensing point CP is
supplied to an optical system chamber OC that accommodates the
optical system 50. The optical system chamber OC is exhausted by a
vacuum pumping system and maintains a predetermined degree of
vacuum. The optical system 50 includes, for example, a reflective
mirror 52 and an optical integrator 54. In the instant embodiment,
the EUV light EL is reflected by the reflective mirror 52, incident
upon the optical integrator 54 and becomes an uniformly
illumination light.
[0041] Although the generating chamber GC is exhausted by the
vacuum pumping system as above-mentioned, the Xe gas as the plasma
generating gas supplied from the first supply pipe 16 exists. The
Xe gas passes through the debris filter 30 and flows into the
condensing chamber CC. Moreover, the Xe gas and the Ar gas as the
buffer gas supplied from the second supply pipe 26 flow into the
optical system chamber OC via an aperture AP formed between the
condensing chamber CC and the optical system chamber OC described
later.
[0042] The gas is exhausted in a position (chamber) introduced gas
and an inflow of the gas to other position (other chambers) is
minimized to prevent an absorption of the EUV light EL by the
plasma generating gas and the buffer gas. Therefore, a gas
conductance of the aperture (opening) formed in a boundary of each
chamber is made small and a differential pumping needs to be
executed.
[0043] In the differential pumping between the condensing chamber
CC and the optical system chamber OC, a pressure of the optical
system chamber OC can be set to almost 1/10 to 1/100 of a pressure
of the condensing chamber CC by setting the aperture AP to the
almost same size as the condensing point CP.
[0044] However, the debris filter 30 is provided between the
generating chamber GC and the condensing chamber CC and an opening
formed by the debris filter 30 becomes large to introduce a lot of
the EUV light EL to the condensing mirror 22. Therefore, a pressure
reduction between the generating chamber GC and the condensing
chamber CC is not so remarkable as the differential pumping between
the condensing chamber CC and the optical system chamber OC.
[0045] Then, the instant embodiment reduces the density of impurity
(hydrocarbon) included in the plasma generating gas and the buffer
gas by the first purity improving part 14, the second purity
improving part 24, the first supply pipe 16 and the second supply
pipe 26. Thereby, when the plasma generating gas and the buffer gas
flow into the condensing chamber CC and the optical system chamber
OC, the adhesion of the carbon to the optical system can be reduced
and prevent a reduction of the reflectance and an occurrence of
non-uniformly light intensity.
[0046] Referring to experiment data shown in Table 1, a description
will be given of effects of the present invention.
[0047] Table 1 shows the density of the hydrocarbon compound in the
light source chamber LC and a reduction rate of the reflectance of
Si/Mo multilayer film sample mirror irradiated by the EUV light EL
in conditions A to C. Here, the condition A (the present invention)
uses the first and second supply pipes 16 and 26 consisted of
stainless steel and uses the gas filter as the first and second
purity improving parts 14 and 24. The condition B uses the first
and second supply pipes 16 and 26 consisted of stainless steel and
does not provide the first and second purity improving parts 14 and
24. The condition C uses the Teflon tube as the first and second
supply pipes 16 and 26 of an outside of the light source chamber LC
and uses the stainless steel as the first and second supply pipes
16 and 26 of an inside of the light source chamber LC. The
condition C does not provide the first and second purity improving
parts 14 and 24.
[0048] In the conditions A to C, the following is the same. A
length of the first supply pipe 16 and second supply pipe 26 is 3.3
m. A flow rate of the plasma generating gas (Xe gas) is 80 sccm. A
flow rate of the buffer gas (Ar gas) is 200 sccm. The density of
the hydrocarbon compound in the Xe tank is 2 ppm. The density of
the hydrocarbon compound in the Ar tank is 500 ppb. The Si/Mo
multilayer film sample mirror is provided near the condensing
mirror 22 of between the condensing mirror 22 and the condensing
point CP. An initial reflectance of the Si/Mo multilayer film
sample mirror is 64.2%. A pressure of the light source chamber LC
is 0.8 Pa. The density of the hydrocarbon analyzed the gas that
flows into the optical system chamber OC from the light source
chamber LC by a quadrupole mass spectrometer connected to the
optical system chamber OC. The condition analyzed the gas to the
light source chamber LC by a gas chromatograph mass spectrometer.
TABLE-US-00001 TABLE 1 Condition A Composition (present invention)
Condition B Condition C Hydrocarbon 6 ppb 700 ppb 6.6 ppm compound
density Reflectance 0.2%/100 hour 2.6%/10 hour 19%/10 hour
reduction Rate of sample mirror in wavelength of 13.5 nm/
irradiation time
[0049] Referring to Table 1 the present invention (condition A)
remarkably improves the reduction of the reflectance of the Si/Mo
multilayer film sample mirror. Since the reduction of the
reflectance of the Si/Mo multilayer film sample mirror is mainly
caused by the adhesion of the contaminant (carbon), the reduction
of the grazing incidence mirror that does not use the multilayer
film remarkably improves. In other words, the present invention can
reduce the adhesion of the contaminant to the optical element that
is provided a reached area of the gas from the light source chamber
LC, such as the condensing mirror 22 and the reflective mirror 52
in the optical system 50 (illumination optical system mirror and
projection optical system mirror). Thereby, the reduction of the
reflectance of the optical element can be remarkably improved.
[0050] Particularly, although the adhesion of the contaminant to
the optical element in the illumination optical system causes the
decrease of the throughput by the reduction of the reflectance, the
non-uniformly light intensity by a change of an optical
performance, and the decrease of the resolution, the present
invention prevents these. The adhesion of the contaminant to the
optical element in the projection optical system causes the
decrease of the throughput by the reduction of the reflectance.
Moreover, although a running cost remarkably increases because the
projection optical system is very expensive, the present invention
prevents these.
[0051] Thus, the present invention can use the optical element in
the illumination optical system and the projection optical system
for long time, prevent the decrease of the throughput and
resolution and provide an economical exposure apparatus that
achieves superior exposure performance.
[0052] The inventor discovered that almost proportional
relationship exists in between the density of the hydrocarbon
compound and the reduction rate of the reflectance of the mirror.
For example, referring to Table 1, if the EUV light EL is
irradiated for 100 hours, it is necessary to control the density of
the hydrocarbon compound in the light source chamber to 300 ppb
(preferably, 30 ppb) or less to control the reduction rate of the
reflectance of the mirror to 10% or less. If the reflectance of the
mirror in the illumination optical system reduces, it is necessary
to exchange the mirror or clean the mirror. Thereby, it is
necessary to stop an operation of the exposure apparatus.
Therefore, controlling the hydrocarbon compound in the light source
chamber (particularly, the condensing chamber) to 300 ppb or less
is a necessary condition for the operation of the exposure
apparatus. However, if an operation stop time of the exposure
apparatus is long or the cost of the mirror to exchange is
expensive, the density of the hydrocarbon compound is controlled to
30 ppb or less and the reduction of the reflectance to the
operation of 1000 hours is controlled to 10% or less. The density
of the hydrocarbon included in the Xe gas supplied from the light
source chamber is preferably controlled to 300 ppb or less to
control the density of the hydrocarbon compound in the light source
chamber to 300 ppb or less. Moreover, the density of the
hydrocarbon included in the Xe gas supplied from the light source
chamber is preferably controlled to 30 ppb or less to control the
density of the hydrocarbon compound in the light source chamber to
30 ppb or less.
[0053] If the pressure of the light source chamber LC can be made
low by a exhaust system with large exhaust performance, even if the
density of the hydrocarbon compound of the plasma generating gas
and the buffer gas is larger than 300 ppb, the reduction of the
reflectance can be controlled. However, in actually, the pressure
of the light source chamber LC becomes about 1.times.10.sup.-1 Pa
to 10 Pa irrespective of the method of the light source by a
generation condition of the plasma PL, a realistic size of the
chamber and a restriction of the exhaust system conductance
according it. Therefore, a relationship between the density of the
hydrocarbon compound and the reduction of the reflectance of the
mirror (optical element) hardly changes irrespective of the method
of the light source.
[0054] In the condensing mirror 22, if the dispersed debris is a
lot, a progress of the adhesion of the contaminant becomes slow.
However, since the reduction rate of the reflectance of the Mo/Si
multilayer film sample mirror in the instant experiment and the
reduction rate of the reflectance of the reflective mirror 52 in
the optical system 50 are almost the same, the amount of the debris
is not an amount that affects the adhesion of the contaminant.
[0055] The instant embodiment explained the density of the
hydrocarbon compound in the plasma generating gas and the buffer
gas that are gas necessary to the emission of the plasma PL.
However, the density of the hydrocarbon compound is preferably
reduced in a gas that is supplied expect when the plasma PL is
emitted (for example, a nitrogen gas used for release of the
chamber for a maintenance). Such gas remains in the chamber
immediately after beginning to vacuum-exhaust the chamber.
[0056] If the light source apparatus 1 is a laser plasma light
source, the reduction of the reflectance of the optical element can
be similarly improved by controlling the density of the hydrocarbon
compound included in the target material and the density of the
hydrocarbon compound included in the buffer gas.
[0057] Next, referring to FIG. 2, a description will be given of a
light source apparatus 1A that is variation of the light source
apparatus 1. The light source apparatus 1A is deferent from the
light source apparatus 1 in a structure of a plasma generating part
10A. Here, FIG. 2 is a schematic sectional view of the light source
apparatus 1A that is variation of the light source apparatus 1
shown in FIG. 1.
[0058] The light source apparatus 1A is typically a discharge
plasma light source. The plasma generating part 10A evaporates a
tin by irradiating a laser beam LL condensed by a condensing lens
19 to a tin rod SR provided in the generating chamber GC, and
generates a plasma PL using a tin vapor (working gas) as the plasma
generating gas.
[0059] The tin rod SR uses a high purity tin. The hydrocarbon is
easily separated by a specific gravity difference between the tin
and the hydrocarbon in a liquid that is a molten state of a
purification process. Therefore, the tin rod SR does not include
the hydrocarbon compound. The tin rod SR uses a cleaned tin so that
the hydrocarbon compound does not adhere to the surface. Therefore,
the hydrocarbon compound does not generate by the evaporation of
the tin.
[0060] On the other hand, the Ar gas as the buffer gas is similar
to the light source apparatus 1 and the density of the hydrocarbon
compound becomes 30 ppb or less by the second purity improving part
24 and the second supply pipe 26.
[0061] Thus, the light source apparatus 1A can prevent the
reduction of the reflectance of the optical element and the
non-uniformly light intensity, prevents the decrease of the
throughput and the resolution, and can provide an economical
exposure apparatus that achieves superior exposure performance.
[0062] Referring to FIG. 3, a description will be given of an
exemplary exposure apparatus 300 that applies the light source
apparatus 1 or 1A. Here, FIG. 3 is a schematic sectional view of
the exposure apparatus 300 according to one aspect of the present
invention.
[0063] The inventive exposure apparatus 300 uses the EUV light
(with a wavelength of, e.g., 13.4 nm) as illumination light for
exposure, and exposes onto a plane 340 a circuit pattern of a mask
320, for example, in a step-and-scan manner or step-and-repeat
manner. This exposure apparatus is suitable for a lithography
process less than submicron or quarter micron, and the present
embodiment uses the step-and-scan exposure apparatus (also referred
to as a "scanner") as an example. The "step-and-scan manner", as
used herein, is an exposure method that exposes a mask pattern onto
a wafer by continuously scanning the wafer relative to the mask,
and by moving, after a shot of exposure, the wafer stepwise to the
next exposure area to be shot. The "step-and-repeat manner" is
another mode of exposure method that moves a wafer stepwise to an
exposure area for the next shot every shot of cell projection onto
the wafer.
[0064] Referring to FIG. 3, the exposure apparatus 300 includes an
illumination apparatus 310, a mask stage 335 mounted with the mask
330, a projection optical system 340, a wafer stage 355 mounted
with the plate 350, an alignment detecting mechanism 360, and a
focus position detecting mechanism 370.
[0065] As shown in FIG. 3, at least the optical path through which
the EUV light travels (or the entire optical system) should
preferably be maintained in a vacuum chamber VC, since the EUV
light has low transmittance to the air and causes contaminations as
a result of response to components of residual gas (or polymer
organic gas).
[0066] The illumination apparatus 310 illuminates the mask 330
using the EUV light that has a wavelength of, for example, 13.4 nm
and an arc shape corresponding to an arc-shaped field of the
projection optical system 340, and includes the light source
apparatus 1 and an illumination optical system 314.
[0067] Any structure as described above is applicable to the light
source apparatus 1, and a detailed description thereof is omitted.
While FIG. 3 uses the light source apparatus 1 shown in FIG. 1,
such a structure is exemplary, and the present invention is not
limited to this. For example, the light source apparatus 1A shown
in FIG. 2 may be used.
[0068] The illumination optical system 314 includes a reflective
mirror 314a and an optical integrator 314b. The reflective mirror
314a reflects the EUV light EL supplied from the light source
apparatus 1 and introduce the EUV light EL to a subsequent optical
element (optical system). The optical integrator 314b uniformly
illuminates the mask 330 with a predetermined aperture. The
illumination optical system 314 further includes an aperture at a
position conjugate with the mask 330, which limits an illumination
area of the mask 330 to an arc shape.
[0069] The mask 330 is a reflection mask, and has a circuit pattern
(or image) to be transferred. The mask 330 is supported and driven
by the mask stage 335. The diffracted light emitted from the mask
330 is projected onto the plate 350 after reflected by the
projection optical system 340. The mask 330 and the plate 350 are
arranged optically conjugate with each other. Since the exposure
apparatus 300 is a scanner, the mask 330 and plate 350 are scanned
to transfer a reduced size of a pattern of the mask 330 onto the
plate 350.
[0070] The mask stage 335 supports the mask 330 and is connected to
a moving mechanism (not shown). The mask stage 335 may use any
structure known in the art. The moving mechanism (not shown) may
includes a linear motor etc., and drives the mask stage 335 at
least in a direction X and moves the mask 330. The exposure
apparatus 300 synchronously scans the mask 330 and the plate 350.
Here, X is a scan direction on the mask 330 or the plate 350, Y is
a direction perpendicular to it, and Z is a perpendicular direction
on the surface of mask 330 or the plate 350.
[0071] The projection optical system 340 uses plural reflective
mirrors (multilayer mirrors) 342 to project a reduce size of a
pattern of the mask 330 onto the plate 350. The number of
reflective mirrors 342 is about four to six. For wide exposure area
with the small number of mirrors, the mask 330 and plate 350 are
simultaneously scanned to transfer a wide area that is an arc-shape
area or ring field apart from the optical axis by a predetermined
distance. The projection optical system 340 has a NA of about 0.2
to 0.3.
[0072] The instant embodiment uses a wafer as the plate 350 to be
exposed, but it may include a spherical semiconductor and liquid
crystal plate and a wide range of other plates to be exposed.
Photoresist is applied onto the plate 350.
[0073] The wafer stage 355 supports the plate 350 via a wafer
chuck. The wafer stage 355 moves the plate 350, for example, using
a linear motor in XYZ directions. The mask 330 and the plate 350
are synchronously scanned. The positions of the mask stage 335 and
wafer stage 355 are monitored, for example, by a laser
interferometer, and driven at a constant speed ratio.
[0074] The alignment detecting mechanism 360 measures a positional
relationship between the position of the mask 330 and the optical
axis of the projection optical system 340, and a positional
relationship between the position of the plate 350 and the optical
axis of the projection optical system 340, and sets positions and
angles of the mask stage 335 and the wafer stage 355 so that a
projected image of the mask 330 may accord with the plate 350.
[0075] The focus position detecting mechanism 370 measures a focus
position on the plate 350 surface, and controls over a position and
angle of the wafer stage 355 always maintains the plate 350 surface
at an imaging position of the projection optical system 340 during
exposure.
[0076] In exposure, the EUV light EL emitted from the illumination
apparatus 310 illuminates the mask 330, and images a pattern of the
mask 330 onto the plate 350 surface. The instant embodiment uses an
arc or ring shaped image plane, scans the mask 330 and plate 350 at
a speed ratio corresponding to a reduction rate to expose the
entire surface of the mask 330. The light source apparatus 1 in the
illumination apparatus 310 used for the exposure apparatus 300 can
prevent the reduction of the reflectance and non-uniformly light
intensity of the optical element in the illumination optical system
and the projection optical system. Therefore, the exposure
apparatus 300 can provide devices (such as semiconductor devices,
LCD devices, image pickup devices (e.g., CCDs), and thin film
magnetic heads) with a high throughput and good economical
efficiency.
[0077] Referring now to FIGS. 4 and 5, a description will be given
of an embodiment of a device fabrication method using the above
mentioned exposure apparatus 300. FIG. 4 is a flowchart for
explaining how to fabricate devices (i.e., semiconductor chips such
as IC and LSI, LCDs, CCDs, and the like). Here, a description will
be given of the fabrication of a semiconductor chip as an example.
Step 1 (circuit design) designs a semiconductor device circuit.
Step 2 (mask fabrication) forms a mask having a designed circuit
pattern. Step 3 (wafer making) manufactures a wafer using materials
such as silicon. Step 4 (wafer process), which is also referred to
as a pretreatment, forms the actual circuitry on the wafer through
lithography using the mask and wafer. Step 5 (assembly), which is
also referred to as a post-treatment, forms into a semiconductor
chip the wafer formed in Step 4 and includes an assembly step
(e.g., dicing, bonding), a packaging step (chip sealing), and the
like. Step 6 (inspection) performs various tests on the
semiconductor device made in Step 5, such as a validity test and a
durability test. Through these steps, a semiconductor device is
finished and shipped (Step 7).
[0078] FIG. 5 is a detailed flowchart of the wafer process in Step
4. Step 11 (oxidation) oxidizes the wafer's surface. Step 12 (CVD)
forms an insulating layer on the wafer's surface. Step 13
(electrode formation) forms electrodes on the wafer by vapor
disposition and the like. Step 14 (ion implantation) implants ions
into the wafer. Step 15 (resist process) applies a photosensitive
material onto the wafer. Step 16 (exposure) uses the exposure
apparatus 300 to expose a circuit pattern from the mask onto the
wafer. Step 17 (development) develops the exposed wafer. Step 18
(etching) etches parts other than a developed resist image. Step 19
(resist stripping) removes unused resist after etching. These steps
are repeated to form multi-layer circuit patterns on the wafer. The
device fabrication method of this embodiment may manufacture higher
quality devices than the conventional one. Thus, the device
fabrication method using the exposure apparatus 300, and resultant
devices constitute one aspect of the present invention.
[0079] Furthermore, the present invention is not limited to these
preferred embodiments and various variations and modifications may
be made without departing from the scope of the present
invention.
[0080] This application claims a foreign priority benefit based on
Japanese Patent Application No. 2005-200764, filed on Jul. 8, 2005,
which is hereby incorporated by reference herein in its entirety as
if fully set forth herein.
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